Cam Profile for a Hydrostatic Radial Piston Machine, and Hydrostatic Radial Piston Machine

ABSTRACT

A cam profile for a hydrostatic radial piston machine includes lobes positioned along a circumferential direction, each lobe comprising a lobe portion of rising type and a lobe portion of falling type. As the cam profile extends in the circumferential direction, a radial dimension of the cam profile mostly increases in each portion of rising type, and mostly decreases in each portion of falling type Shapes of at least two lobe portions of the same type are different.

This application claims priority under 35 U.S.C. § 119 to patentapplication number EP 17203248.4 filed on Nov. 23, 2017 in Europe, thedisclosure of which is incorporated herein by reference in its entirety.

The present disclosure relates to a cam profile for a hydrostatic radialpiston machine, and to a hydrostatic radial piston machine.

BACKGROUND

Hydrostatic radial piston machines (“machines”) typically comprise aplurality of pistons pushing out via rollers against a cam having aplurality of lobes on the cam's periphery. In addition, machines areknown that can operate in different displacement modes (e.g. two speedoperation); an example is the radial piston motor Rexroth MGR-H. Twospeed operation can be achieved by turning off the pressure supply toonly some of the pistons or lobes. The latter is achieved byinterrupting the pressure to each piston in turn as it passes throughthe angular extent of a predetermined lobe.

It can be desired to provide constant machine displacement per degree ofrotation and this can limit the number of lobes that can be turned off.Specifically, the choice of ratios is limited depending on the number ofpistons and the number of lobes. For example: if the numbers have acommon factor of two (e.g. six lobes and eight pistons) then the naturalratio is 50%. If the common factor is three then the usable naturalratios are 33% and 67%. So the usable natural ratios are determined inaddition by said common factor. Due to this constraint a limited numberof natural ratios are usable, which do not necessarily comprise theratio required for a particular application.

SUMMARY

It is an object of the disclosure to allow a greater choice of ratiobetween reduced- and full-displacement modes (“actual machine ratio”)and to maximize the machine displacement for a given ratio. It is afurther object to optimize the life in particular in a predeterminedrotation direction. The object is achieved by the subject-matter of thedisclosure. Advantageous further developments are subject-matter of theclaims, description, and drawings.

A cam profile for a hydrostatic radial piston machine, according to thedisclosure comprises lobes arranged in a circumferential direction, eachlobe comprising a lobe portion of rising type and a lobe portion offalling type, wherein as the cam profile extends in a circumferentialdirection, its radial dimension mostly increases in each portion ofrising type, and mostly decreases in each portion of falling type; theshapes of at least two lobe portions of the same type are different.Therefore when the machine operates in reduced displacement mode andcertain lobes are turned off, the turned off lobes can have differentshapes from the always-tuned-on lobes, giving greater choice ofperformance characteristics e.g. ratio between full-displacement andreduced displacement mode. Also the shapes of each portion can now beadapted to suit the various surface wear regimes on the respective lobeportions, in particular in view of any preferred rotation direction.Machine life can be improved.

Preferably the lobe depths of at least two lobe portions of the sametype may be different. Since lobe depth influences displacement, agreater choice of actual machine ratios is possible. So the actualmachine ratio can be varied from the natural ratio by making the lobeswhich get turned off different depth to the lobes which remain on.

Preferably the angular extents of at least two lobes may be different.Since contact stress on a lobe depends partly on the lobe's angularextent, the balance in wear performance between the always-turned-<lnlobes and of the lobes that are turned off in reduced displacement modecan be adapted according to operational requirements, and machine lifecan be optimized.

Further preferably the angular extents of at least two lobe portions ofthe same type may be different. The balance in wear performance betweendirections of rotation, and also the actual machine ratio, can beadapted with independence and according to operational requirements.

Preferably the cam profile may comprise at least one first lobe and atleast one second lobe, wherein each second lobe has a greater angularextent and a greater lobe depth than each first lobe. Therefore thecurvature of a deep lobe is kept low, contact stresses on the lobe arekept low, and the machine life is improved.

Preferably the lobes may be arranged in a symmetrical fashion, such asrotationally symmetric, further preferably alternating, with respect totheir angular extents. Rotational imbalances and vibration are kept low;the construction is simplified.

According to a preferable embodiment the cam profile may additionallycomprise sectors into which the lobes are divided by whole lobes,wherein lobes in at least one sector have greater angular extents thanlobes in at least one other sector. In this way at least one reduceddisplacement mode can be provided in which the lobes of one of thesectors are turned off. The angular extents can now be configured tomaintain constant motor displacement per degree of rotation, providingsmoothness of operation (e.g. reduced ripple torque and/or vibration);actual machine ratios other than the natural ratios are achievablewithout having to reduce lobe depths; the choice of lobes for turningoff is greater, and machine displacement can be enhanced. Furtherpreferably a sector having first lobes and no second lobes, and anothersector having second lobes and no first lobes, may join directly attheir ends, wherein the second lobes have greater angular extent, andpreferably also greater lobe depth, than the first lobes. The aboveadvantages are achieved with a simplified construction.

Preferably the angular extents of at least two lobe portions ofdifferent type may be different. Thus wear performance can be enhancedin one direction, for one or both operating modes. For example it ispossible to provide a longer-life machine having a mode combining slowspeed with reverse rotation.

A cam profile for a hydrostatic radial piston machine, according to thedisclosure comprises lobes arranged in a circumferential direction, eachlobe comprising a lobe portion of rising type and a lobe portion offalling type, wherein as the cam profile extends in a circumferentialdirection, its radial dimension mostly increases in each portion ofrising type and mostly decreases in each portion of falling type; theangular extents of at least two lobe portions of different type aredifferent. The machine can have enhanced wear performance in onedirection.

Preferably one of above cam profiles may be configured so that, as itextends in a circumferential direction, its radial dimension increasesonly in each portion of rising type, and/or decreases only in eachportion of falling type.

Preferably the lobes of one of above cam profiles may be directly joinedtogether.

A hydrostatic radial piston machine, according to the disclosurecomprises a cam body having the cam profile. The advantages indicatedabove can be achieved in a hydrostatic radial piston machine.

A hydrostatic radial piston machine, according to the disclosure,comprises a cam body having a cam profile according to the preferableembodiment; and pistons rotatable relative to and engaging with the camprofile, wherein the number of pistons engaging with at least one sectordoes not change with rotation angle. The advantages for the preferableembodiment can be achieved in a hydrostatic radial piston machine.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferable exemplary embodiments of the disclosure are explained in moredetail in the following, with the help of schematic drawings, whereinlike numerals are used to represent like elements and wherein:

FIG. 1 shows a hydrostatic radial piston machine, according to a firstembodiment serving as background to the disclosure;

FIG. 2 shows a cam profile of a hydrostatic radial piston machine of asecond embodiment;

FIG. 3 shows a cam profile of a hydrostatic radial piston machine of athird embodiment;

FIG. 4 shows a cam profile of a hydrostatic radial piston machine of afourth embodiment; and

FIG. 5 shows a cam profile of a hydrostatic radial piston machine of afifth embodiment.

DETAILED DESCRIPTION

A first embodiment serving as background to the disclosure is describedin the following, with reference to FIG. 1 which shows a hydrostaticradial piston machine 401. The machine 401 is executed as a motor havinga rotor comprising a cylinder block 403 rotatable in a stationary andannular cam body 402 which may preferably be a housing element. Thecylinder block 403 comprises a plurality of equispaced cylindersarranged around the axis of rotation with their open ends directedradially outwards, the cylinders forming a star shape around therotation axis. The angles between the cylinders are preferably fixed.The cylinder block 403 has a splined hole provided at its center fortransferring torque to and from an external apparatus. A piston 404 isslidably accommodated in each cylinder, so the pistons 404 are arrangedin a symmetric star shape around the rotation axis. Each piston 404confines together with the respective cylinder a working chamber 430communicable alternately with high pressure or low pressure lower thanthe high pressure. To this end each cylinder is provided with a timinghole (cylinder hole 407, shown hatched in FIG. 1) to allow the chamber430 to be (de)pressurized. The cylinder holes 407 cooperate with aplurality of timing holes (distributor holes 408) of a flu iddistributor 406. The cylinder holes 407 and the distributor holes 408are provided at a pitch circle diameter so as to allow the holes tooverlap during rotation.

The cam body 402 has an undulating cam surface on its inner periphery soas to comprise identical lobes which are equispaced around the rotationaxis. Each piston 404 is provided with a rolling element (which is aroller 5 in the present embodiment) provided on the radially outer endof the piston 404. The pistons 404, under appropriate pressurization,can radially actuate so as to engage with the cam surface via therollers 405. Thus the rollers 405 are supportable on the cam surface soas to roll thereon as the cylinder block 403 rotates relative to the cambody 402. When the machine operates as a motor the contact forcetransferred to each piston 404 results in a turning force on thecylinder block 403 which then rotates in the direction of arrow 413.When the machine operates as a pump the rotation of the cylinder block403 causes the pistons 404 to reciprocate to generate pressure in theworking chambers 430.

The lobes have uniform lobe depth. “Lobe depth” is understood to meanthe peak-to-trough radial dimension of the lobe, i.e. measured from thelobe's furthest point from the rotation axis to the lobe's nearest pointto the rotation axis. Each lobe has a falling portion 412 and a risingportion 422 (shown exemplarily for one lobe in FIG. 1, the referencesigns 412, 422 pointing to dashed lines for indicating the angularextents of the respective portions). When a roller 405 passes throughthe angular extent of the rising portion 422, it is flu idly connectedto high pressure so that it actuates a working stroke. When the roller405 crosses the boundary 414 between the two portions 412, 422 andstarts to pass through the angular extent of the falling portion 412, itbecomes fluidly connected to low pressure so that it actuates a returnstroke in the opposite radial direction to the working stroke. Thenumber of high-pressure distributor holes (shown as cross-hatchedcircles) is equal to the number of low-pressure distributor holes (shownas unfilled circles), and are each equal to the number of lobe portions412, 422, so that one high-pressure distributor hole 408 is assigned toone portion 422, and one low pressure distributor hole 408 (e.g. 408 a)is assigned to the other portion 412. Angular extent of a lobe portionis understood to mean the angle between a minimum radial point to anadjacent maximum radial point, or vice versa.

For example when the machine is a motor, the working stroke of a piston404 is one in which the volume of the working chamber 430 increases.When the machine is a pump, the working stroke of a piston 404 is one inwhich the piston 404 actuates so that the volume of the working chamber430 decreases.

The portions 412, 422 have uniform (the same) angular extent. The pitchof the distributor holes 408 is uniform. The distance between adjacentdistributor holes 408 may be equal to the diameter of each cylinder hole407, or be slightly larger, e.g. to allow for tolerances or to reducenoise, so that a section of each lobe portion 412, 422 is inactive. Thesection may be at a boundary 414, 415 between lobe portions 412, 422,and may optionally have an angular extent of about one degree, or lessor more than one degree; the cam profile may be adapted accordingly. Thetiming holes 407, 408 may be circular, and their sizes and pitch circlediameter may be adapted in view of reducing flow resistance.

Therefore as the cylinder block 403 rotates, each cylinder hole 407 isexposed to high/low pressure based on the position of each piston 404relative to a lobe portion 412, 422. More specifically, the distributorholes 8 are located and sized such that when the cylinder block 403rotates, a cylinder hole 407 starts to overlap with a distributor hole408 (e.g. 408 a) as a roller 405 reaches the start of a lobe portion412. The overlap finishes as the roller 405 leaves that portion 412.When executed as a motor the aforementioned timing of high and lowpressure urges the rollers 405 against the cam profile so as to create aturning force. When executed as a pump, the cam profile's urging of thepiston 404 into its cylinder under rotation causes fluid pressurization.The machine is configured to operate in a full-displacement mode or areduced displacement mode, and to change between these two. In thefull-displacement mode all lobes and pistons 404 are turned on, i.e. thepistons 404 are each pressurized so as to bear on each lobe. In thereduced-displacement mode a proportion of the lobes are turned off, thatis to say as each piston 404 passes through the angular extent of one ofthe turned-off lobes, its cylinder is not fluidly connected to apressure source but instead fluid can recirculate. The totaldisplacement of the pistons 404 for a predetermined rotation is reducedin this so-called “reduced-displacement mode”.

FIG. 1 shows also a hydraulic circuit 416 comprising a distributor 406which includes four mutually isolated galleries 409 are each formed as agroove. The distributor holes are fluidly connected to the galleries 409via channels 410, so that each gallery 409 is in fluid connection withthree distributor holes 408 as well as to one of two working ports A, B,wherein one is configurable as a high pressure port and the other is aconfigurable as a low pressure port. Two galleries 409 are fluidlyconnected to these ports via a valve 411. The valve 411 has twosimultaneously interruptible flow paths. In full-displacement mode thevalve 411 is set to allow flow, while in reduced displacement mode thevalve 411 is set to interrupt the flow causing some lobes to turn off.

FIG. 2 shows the cam profile according to a second embodiment.Differences from the first embodiment are indicated in the following.

The cam body 2 comprises first lobes 18 and second lobes 20 having adepth 28 greater than the depth 26 of the first lobes 18, and that arearranged rotationally symmetrically, more specifically in an alternatingcircumferential pattern. The angular extents of the lobes are uniform;the lobe depths are non-uniform. Each lobe comprises a falling portion12 and a rising portion 22 (shown exemplarily for one lobe in FIG. 2).

The rotor elements and the hydraulic circuit correspond with the rotorelements and hydraulic circuit 416 of the embodiment of FIG. 1.

The second embodiment has the following advantages. The actual machineratio (the ratio between full and partial displacement) is now dependentnot just on the natural ratio but also on the proportions of the lobedepths 26, 28. So an actual machine ratio can be more freely selectedthan if the lobes were to have uniform depth. To demonstrate theadvantage, a modification to the present embodiment is now described.The number of pistons is ten and the number of lobes is eight, giving acommon factor between these of two which yields a usable natural ratioof 50%, wherein four of the eight lobes are turned on only infull-displacement mode. An actual machine ratio of 60% is now possibleby reducing the lobe depths of some lobes so that the total motordisplacement is 83% of the theoretical maximum.

FIG. 3 shows schematically a cam profile (solid line) on a cam body 102,according to a third embodiment, comprising first 118 and second 120lobes having have the same non-uniformity in lobe depth 126, 128 as thesecond embodiment (shown in FIG. 3 with a dash-dot line). Differencesfrom the second embodiment are explained in the following. The secondlobes 120 have an angular extent greater than (are wider than) the firstlobes 118, i.e. the pitch between the lobe portions is non-uniform,measured as the angle between the mid-points of two adjacent lobeportions. Each lobe comprises a falling portion 112 and a rising portion122 which are indicated exemplarily for one lobe in FIG. 2.

The third embodiment differs further from the first and secondembodiments in that the distributor holes of the third embodiment arenot equispaced but are arranged in a pattern corresponding to thenon-uniform pitch of the lobe portions 112, 122. In this way anappropriate timing of high-pressurization and low-pressurizationcorresponding to the different angular extents of the lobes 118, 120 isachieved. The present exemplary embodiment has the following additionaladvantages. Increasing the angular extent of a second lobe 120 reducessurface wear due to its reduced curvature, so motor life increases.Decreasing the angular extent of the first lobes 118 will not reducemotor life substantially because the first lobes 118 can be configuredto be turned off in reduced-displacement mode, and so operate for only aproportion of the machine's operating life. Thus the expected lives ofthe two lobe types 118, 120 are brought closer and the total cam life isimproved. This will also decrease wear on the rollers and the pistons,and therefore further increase machine life generally.

The advantage of increased motor life through wear optimization of thelobe-types can be achieved even if the lobes have uniform depths, oreven if the deeper lobes are also the narrower lobes. Preferably thelobes that are always turned on may have a greater angular extent thanother lobes. Since some of the lobes will be turned off in reduceddisplacement mode, it may be advantageous for these to have a lowerrunning life in order to optimize full motor life. This is achieved byfurther modification of the angular extents of the various lobes.

FIG. 4 shows schematically a cam profile (solid line) according to afourth embodiment, comprising first 218 and second 220 lobes havinggreater angular extent than the first lobes 218. The differences fromthe third embodiment are explained in the following.

The lobes preferably have uniform depth. The lobe profile is dividedcircumferentially into a first sector 232 comprising first lobes 218,and a second sector 234 (indicated with a dotted area in FIG. 4)comprising second lobes 220. The first sector 232 does not comprise anysecond lobes, and the second sector 234 does not comprise any firstlobes 218. In other words the cam profile is divided by whole lobes intotwo sectors. Preferably one sector (e.g. first sector 232) may beassigned to always-turned-on lobes 18 and another sector (e.g. secondsector 234) may be assigned to lobes 20 turned on only infull-displacement mode. The lobes 220 of the second sector 234 have amean average angular extent which is greater than the mean averageangular extent for the lobes 218 of the first sector 232. The fallingportion and the rising portion of each lobe are indicated exemplarilyfor one lobe in FIG. 4 with the reference signs 212 and 222respectively. A comparative example comprising six lobes having uniformlobe depths and uniform angular extents is represented with a dash-dotline. Each piston is represented in FIG. 4 by a respective roller 205a-205 h.

The machine 201 of the fourth embodiment may be controlled by thehydraulic circuit of the third embodiment, with the followingdifferences. The distributor holes for the lobes 220 in the secondsector 234 are in communication with the interruptible galleries 409.The remaining distributor holes are fluidly connected to the remaininggalleries 409; the routing of the channels 410 is adapted accordingly.The distributor holes are arranged to correspond with the angularextents of each lobe portion 212, 222.

The present embodiment has the following further advantages in additionto those of the third embodiment. In the third embodiment therequirement of constant motor displacement per degree of rotation limitsthe usable natural ratios to 50%; in order to achieve an actual machineratio that differs from 50% it is necessary to reduce the depths of somelobes, which limits the total motor displacement. However the presentembodiment can operate with a natural ratio of 67%, yet the requirementof constant motor displacement per degree of rotation is nonethelessfulfilled, without having to reduce any of the lobe depths. So byvarying the angular extent of some lobes it is possible to ensure thateach sector has a constant number of pistons active for any rotationangle. For example as one roller 205 f leaves the second sector 234 andenters the first sector 232, another roller 205 a leaves the firstsector 232 and enters the second sector 234, assuming counter-clockwiserotation, represented by the arrow 213.

So constant motor displacement is achieved by slightly increasing theangular extent of lobes 220 in the second sector 234 and slightlydecreasing the angular extent of lobes 218 in the first sector 232,relative to the comparative example of equal extents.

In summary, it is possible to turn off different numbers of lobes (andthus access a greater range of natural ratios) whilst maintainingconstant displacement per degree of rotation in both full and reduceddisplacements. This is achieved by setting design characteristics in away which does not require additional structural elements. The designand manufacture of the machine 201, wherein a non-standard number oflobes can be turned off, is simplified. The lobe depths may be adaptedin view of further modifying lobe life and/or actual machine ratio. Themachine of the present embodiment can have a higher total machinedisplacement for a predetermined actual machine ratio.

A fifth embodiment will now be described with reference to FIG. 5 whichshows a cam profile (solid line) of a cam body 302 and rollers 305representing the pistons. As in the first embodiment: the lobes haveuniform depths and uniform angular extents so as to share a common depthand a common width; and each lobe has a falling portion 312 in which aroller 305 engaging therewith moves radially inwards as said roller 305rotates with its respective piston in one direction 313, and a risingportion 322 in which a roller 305 engaging therewith moves radiallyoutwards as said roller 305 rotates with its respective piston in theone direction 313.

Differences from the first embodiment are indicated in the following.The machine is configured to rotate in one direction (clockwise 313)with increased motor life and/or performance compared to the otherdirection. The rising portions 322 each have greater angular extent thanthe angular extent of each falling portion 312. In FIG. 5 the referencesigns 312, 322 point to dashed lines which indicate the extents of therespective portions 312, 322. When the machine is a motor, each pistonactuates under high pressure when its corresponding roller 305 passesthrough a rising portion 322, and actuates under a low pressure lowerthan the high pressure when its corresponding roller 305 passes througha falling portion 312. Preferably the rising portions 322 share a commonangular extent, and the falling portions 312 share a common angularextent. In this way the portions 312, 322 of each lobe are non-uniformwith respect to angular extent, although the lobes themselves may beuniform with respect to each other.

The profile of the present embodiment may be used with a hydrauliccircuit of the third embodiment, adapted as follows. The pitch of thedistributor holes are non-uniform so as to correspond to the non-uniformpitch of the portions 312, 322. Alternatively the machine of the presentembodiment may be operated in a reduced-displacement mode by turning offpressure to predetermined pistons.

The cam profile of the first embodiment is shown with a dash-dot line inFIG. 5 as a comparative example.

The present exemplary embodiment has the following advantages. When themachine is provided as a motor and rotates in a direction 313, thepiston actuates radially outward through the rising portion 322 underhigh pressure higher than the pressure in the falling portion 312. Thiswill tend to increase the contact stresses on the rising portions 322.The angular extent of the rising portion 322 is comparatively larger,resulting in a reduced curvature of the cam profile. The contact anglebetween the cam surface and the roller 305 is reduced, leading to lowercontact stresses. Therefore the wear on the rising portion 322 isreduced, increasing its operational life, while the wear on the fallingportion 312 is increased, reducing its operational life, but notsubstantially since the contact stresses are already low here, incomparison to the contact stresses in the rising portion 322. Thereforethe respective operational lives of the portions 312, 322 are broughtcloser to each other, and the overall operation life of the cam profilecan be optimized. Machine life and performance in the one direction 313can improved. Total machine life can be improved when the machinerotates in one direction 313 more often than in the other direction. Thepresent embodiment may be combined with any of the other embodiments,e.g. so as to provide non-uniform lobes, wherein the portions of eachlobe have non-uniform angular extents.

The disclosure is not limited to hydrostatic radial piston machines inwhich the number of pistons is greater than the number of lobes by two,but this arrangement (in particular eight pistons and six lobes) canbring benefits of simplicity of construction and operationalperformance.

A “lobe” according to the disclosure need not be understood to be only aradially rising portion followed by a radially falling portion of thecam profile in the direction of rotation. A lobe may equally beunderstood to be a radially falling portion followed by a radiallyrising portion of the cam profile in either circumferential direction.Further optionally the pistons, cylinders and rollers may be providedradially outside of a cam body whose cam surface is on its outerperiphery. Further optionally the cylinders may be provided asindividual elements rather than in an integral cylinder body. Furtheroptionally the pistons may bear directly on the cam surface, rather thanvia rollers. The machine of the disclosure may be a motor and/or a pump.The disclosure may be configured to operate in two or morereduced-displacement modes.

Disclosed is a cam body for a hydrostatic radial piston machine,including a cam profile comprising lobes arranged in a circumferentialpattern. Each lobe is divided into a rising portion whose radiusincreases along a circumferential direction, and a falling portion whoseradius decreases along the circumferential direction. The portions arenon-uniform, preferably non-uniform in maximum radial depth, and/or inangular extent. Preferably the radial extents of the lobes arenon-uniform and/or their lobe depths are non-uniform.

REFERENCE SIGNS

-   401 . . . hydrostatic radial piston machine-   2; 102; 202; 302; 402 . . . cam body-   403 . . . cylinder block-   404 . . . piston-   205; 305; 405 . . . roller-   406 . . . distributor-   407 . . . cylinder hole-   408, 408 a . . . distributor hole-   409 . . . gallery-   410 . . . channels-   411 . . . valve-   12; 112; 212; 312; 412 . . . falling lobe portion-   213; 313; 413 . . . a direction of rotation-   414 . . . start of overlap between rotor hole and distributor hole    408 a-   415 . . . end of overlap between rotor hole and distributor hole 408    a-   416 . . . hydraulic circuit-   18; 118; 218; 318 . . . first lobe-   20; 120; 220 . . . second lobe-   22; 122; 222; 322; 422 . . . rising lobe portion-   26; 126 . . . depth, first lobe-   28; 128 . . . depth, second lobe-   430 . . . working chamber-   A . . . working port-   B . . . working port

1. A cam profile for a hydrostatic radial piston machine, comprising: aplurality of lobes positioned along a circumferential direction, each ofthe plurality of lobes including: a lobe portion of rising type; and alobe portion of falling type, wherein as the cam profile extends in thecircumferential direction, a radial dimension of the cam profile mostlyincreases in each lobe portion of rising type, and mostly decreases ineach lobe portion of falling type, and wherein shapes of at least twolobe portions of the same type are different.
 2. The cam profileaccording to claim 1, wherein lobe depths of at least two lobe portionsof the same type are different.
 3. The cam profile according to claim 1,wherein the angular extents of at least two lobes are different.
 4. Thecam profile according to claim 1, wherein: the plurality of lobesincludes at least one first lobe and at least one second lobe, and eachsecond lobe has a greater angular extent and a greater lobe depth thaneach first lobe.
 5. The cam profile according to claim 1, wherein: wholelobes of the plurality of lobes are distributed amongst sectors, andlobes in at least one of the sectors have greater angular extents thanlobes in at least one other of the sectors.
 6. The cam profile accordingto claim 2, wherein angular extents of at least two lobe portions ofdifferent type are different.
 7. A cam profile for a hydrostatic radialpiston machine, comprising: a plurality of lobes positioned along acircumferential direction, each of the plurality of lobes including: alobe portion of rising type; and a lobe portion of falling type, whereinas the cam profile extends in the circumferential direction, a radialdimension mostly increases in each lobe portion of rising type andmostly decreases in each lobe portion of failing type, and angularextents of at least two lobe portions of different type are different.8. A hydrostatic radial piston machine comprising: a cam body including:a cam profile having a plurality of lobes positioned along acircumferential direction, each of the plurality of lobes including: alobe portion of rising type; and a lobe portion of falling type, whereinas the cam profile extends in the circumferential direction, a radialdimension of the cam profile mostly increases in each lobe portion ofrising type, and mostly decreases in each lobe portion of falling type,and wherein shapes of at least two lobe portions of the same type aredifferent.
 9. The hydrostatic radial piston machine according to claim8, wherein: whole lobes of the plurality of lobes are distributedamongst sectors; lobes in at least one of the sectors have greaterangular extents than lobes in at least one other of the sectors; thehydrostatic radial piston machine further comprises pistons rotatablerelative to and engaging with the cam profile, and a number of pistonsengaging with at least one sector does not change with rotation angle ofthe pistons.